Imaging lens

ABSTRACT

A low-cost imaging lens which corrects aberrations properly with a small F-value, ensures high performance with a larger number of constituent lenses and has a more low-profile design than before. The constituent lenses are arranged in the following order from an object side to an image side: a positive (refractive power) first lens having a convex object-side surface near an optical axis; a positive second lens having convex object-side and image-side surfaces near the optical axis; a negative third lens having a concave image-side surface near the optical axis; a fourth lens having at least one aspheric surface; a meniscus fifth lens having a concave object-side surface near the optical axis; a sixth lens as a double-sided aspheric lens; and a negative seventh lens as a double-sided aspheric lens having a concave image-side surface near the optical axis. These constituent lenses are not joined to each other.

The present application is based on and claims priority of Japanesepatent application No. 2013-015291 filed on Jan. 30, 2013, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to imaging lenses which form an image ofan object on a solid-state image sensor such as a CCD sensor or C-MOSsensor used in a compact image pickup device and more particularly toimaging lenses which are built in image pickup devices mounted inincreasingly sophisticated mobile terminals such as smart phones, mobilephones, and PDAs (Personal Digital Assistants), and game consoles andinformation terminals such as PCs.

2. Description of the Related Art

In recent years, the market of tablet multifunctional terminals astypified by smart phones has been rapidly expanding and there is ageneral trend that such terminals incorporate high-performance,high-quality cameras which cope with an increase in the number ofpixels, for example, over 8 megapixels. Since the trend towards cameraswhich cope with an increase in the number of pixels is expected to beaccelerated, the imaging lenses built in image pickup devices arerequired to provide high performance to cope with an increase in thenumber of pixels and also be compact enough to suit low-profile productdesigns. Furthermore, since pixel size becomes smaller with the tendencytoward smaller image sensors and a larger number of pixels, the imaginglenses are strongly expected to provide high brightness.

In addition to many types of imaging lens composed of four lenses(four-element imaging lens) which have been proposed so far, imaginglenses composed of five or six lenses (five-element or six-elementimaging lens) are proposed in order to meet the trend toward higherperformance and more compactness.

For example, JP-A-2007-264180 (Patent Document 1) discloses an imaginglens which includes, in order from an object side, a positive first lenshaving a convex object-side surface, a negative meniscus second lenshaving a concave image-side surface, a positive meniscus third lenshaving a convex image-side surface, a negative fourth lens as adouble-sided aspheric lens having a concave image-side surface near anoptical axis, and a positive or negative fifth lens as a double-sidedaspheric lens.

Also, JP-A-2011-085733 (Patent Document 2) discloses an imaging lenssystem which includes, in order from an object side, a first lens groupincluding a first lens with a convex object-side surface, a second lensgroup including a second lens with a concave image-side surface, a thirdlens group including a meniscus third lens with a concave object-sidesurface, a fourth lens group including a meniscus fourth lens with aconcave object-side surface, and a fifth lens group including a meniscusfifth lens with an aspheric object-side surface having an inflectionpoint, and also discloses an imaging lens composed of six lensesincluding a positive lens having a slightly convex surface on the objectside of the above lens system and a slightly concave surface on itsimage side.

The imaging lens described in Patent Document 1, composed of fivelenses, realizes a high-performance imaging lens system which correctsaxial chromatic aberrations and chromatic aberrations of magnificationand copes with an increase in the number of pixels, by optimizing thelens material and lens surface shapes. However, its total track lengthis as long as about 8 mm and there is difficulty in applying it to anincreasingly low-profile image pickup device. Also, the F-value is about2.8, which is not sufficient to provide high brightness as expected inrecent years.

Patent Document 2 discloses a high-resolution imaging lens composed offive lenses and a high-resolution imaging lens composed of six lenses.The total track length of the five-element imaging lens is about 6 mmand that of the six-element imaging lens is about 6.6 mm, so theseimaging lenses are considered to meet the demand for a low-profiledesign to some extent. However, in this technique, the F-value is about2.8, so it is difficult to provide both high resolution and highbrightness as expected in recent years.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problem and anobject thereof is to realize a high-performance lens system whichcorrects various aberrations properly with a small F-value and provide alow-cost imaging lens which can be more low-profile or thinner thanbefore even though a larger number of constituent lenses are used.

According to an aspect of the present invention, there is provided afixed-focus imaging lens composed of seven lenses to form an image of anobject on a solid-state image sensor, in which the lenses are arrangedin the following order from an object side to an image side: a firstlens with positive refractive power having a convex surface on theobject side near an optical axis; a second lens with positive refractivepower having convex surfaces on the object side and the image side nearthe optical axis; a third lens with negative refractive power having aconcave surface on the image side near the optical axis; a fourth lenshaving at least one aspheric surface; a meniscus fifth lens having aconcave surface on the object side near the optical axis; a sixth lensas a double-sided aspheric lens; and a seventh lens as a double-sidedaspheric lens with negative refractive power having a concave surface onthe image side near the optical axis. The constituent lenses are notjoined to each other.

The above imaging lens uses a larger number of constituent lenses thanthe many imaging lenses proposed so far. Obviously an imaging lens whichuses a larger number of constituent lenses provides higher performance,but it is disadvantageous in achieving thinness and cost reduction. Thepresent invention is intended to meet the need for an imaging lens witha small F-value which provides high performance suitable for an imagesensor handling an increasing number of pixels and which is thinner ormore low-profile than before.

In the above imaging lens, the positive refractive power of the secondlens is stronger than that of the first lens so that sphericalaberrations, astigmatism, and axial chromatic aberrations are corrected,and the second lens has a relatively strong positive refractive power sothat the total track length is shortened. When both the surfaces of eachof the first lens and the second lens have adequate aspheric shapes,various aberrations are corrected properly.

The third lens, which has relatively strong negative refractive power,properly corrects residual axial chromatic aberrations which have notbeen corrected by the first lens and the second lens.

The fourth lens, which plays a major role in correction of aberrations,corrects spherical aberrations, astigmatism, and coma aberrationsthrough at least one aspheric surface thereof and also contributeslargely to reducing astigmatic difference. Since the fourth lens isintended to correct aberrations, it is desirable that its refractivepower be weak. More specifically, it is preferable that its focal lengthbe approximately 1.5 to 2 times longer than the focal length of theoverall optical system of the imaging lens. In addition, when both thesurfaces are aspheric, aberrations are corrected more properly.

The fifth lens is a meniscus lens which has the weakest positive ornegative refractive power in the lens system and has a concave surfaceon the object side. It is responsible for further correction of axialchromatic aberrations, proper correction of chromatic aberrations ofmagnification. It also corrects distortion on the image plane in thearea from a low image height point to a nearly 80% image height point.

Both the surfaces of each of the sixth lens and the seventh lens haveadequate aspheric shapes to control the angle of light rays emitted fromthe fifth lens in the area from the low image height point to themaximum image height point properly to form an image on the image plane.At the same time, these lenses are responsible for final correction ofspherical aberrations in the lens peripheral portion, astigmatism,astigmatic difference, and distortion.

Generally, when the F-value is smaller, the entrance pupil diameter andthe lens effective diameter are larger and the diameter of the flux oflight entering the lens system is larger. This leads to an increase inthe amount of spherical aberrations in the lens peripheral portion andan increase in the amount of off-axial aberrations. Therefore, when theF-value is smaller, means to correct various aberrations must beincreased. In the present invention, the seven constituent lenses areeach designed to have optimum refractive power and adequate asphericsurfaces are formed on specific lens surfaces so as to correctaberrations more effectively. Consequently the lens system in thepresent invention achieves a small F-value, for example, about 1.6,which the existing five-element or six-element imaging lenses could notachieve, and also corrects aberrations properly.

In the present invention, no cemented lenses are used and theconstituent lenses are spaced from each other so that the number ofaspheric surfaces can be increased to enhance performance. Also, plasticmaterial is used as much as possible to reduce cost.

In the present invention, preferably the first lens has a meniscus shapewith a convex surface on the object side near the optical axis and boththe surfaces have aspheric shapes with the peripheral portions curvedtoward the object side. Since the first lens, located nearest to theobject side, has such aspheric shapes, the amount of sphericalaberrations which occur on the peripheral portion of the biconvex secondlens with strong refractive power can be decreased by the asphericshapes of the first lens and field curvature in the area from a nearlymiddle image height point to the maximum image height point can becorrected easily.

Preferably the imaging lens according to the present invention satisfiesconditional expressions (1), (2), and (3) below:

50<νd1<60  (1)

50<νd2<60  (2)

20<νd3<30  (3)

-   -   where    -   νd1: Abbe number of the first lens at d-ray    -   νd2: Abbe number of the second lens at d-ray    -   νd3: Abbe number of the third lens at d-ray

The conditional expression (1) defines an adequate range for the Abbenumber of the first lens, the conditional expression (2) defines anadequate range for the Abbe number of the second lens, and theconditional expression (3) defines an adequate range for the Abbe numberof the third lens. When the positive first and second lenses fall withinthe ranges defined by the conditional expressions (1) and (2)respectively and a low-dispersion material is used for them, chromaticaberrations are suppressed; and when the third lens falls within therange defined by the conditional expression (3), the third lens correctsresidual axial aberrations which have not been corrected by the firstlens and the second lens, without increasing the negative refractivepower of the third lens more than necessary. If the value is below thelower limit of the conditional expression (1) or conditional expression(2), correction of axial chromatic aberrations might be insufficient andif it is above the upper limit, it would be difficult to use aninexpensive material. If the value is below the lower limit of theconditional expression (3), it would be difficult to use an inexpensivematerial and if it is above the upper limit, axial chromatic aberrationscannot be corrected sufficiently.

Preferably the imaging lens according to the present invention satisfiesconditional expressions (4) and (5) below:

50<νd4<60  (4)

20<νd5<30  (5)

-   -   where    -   νd4: Abbe number of the fourth lens at d-ray    -   νd5: Abbe number of the fifth lens at d-ray

The conditional expression (4) defines an adequate range for the Abbenumber of the fourth lens and the conditional expression (5) defines anadequate range for the Abbe number of the fifth lens. When the fourthlens falls within the range defined by the conditional expression (4)and a low-dispersion material is used, chromatic aberrations ofmagnification are suppressed, and when the fifth lens falls within therange defined by the conditional expression (5), chromatic aberrationsof magnification are corrected effectively. If the value is below thelower limit of the conditional expression (4) and the value is above theupper limit of the conditional expression (5), chromatic aberrations ofmagnification would not be corrected sufficiently. If the value is abovethe upper limit of the conditional expression (4) and the value is belowthe lower limit of the conditional expression (5), it would be difficultto use an inexpensive material.

In the present invention, preferably the fourth lens has a biconvexshape near the optical axis and its image-side surface has an asphericshape with a concave surface in the peripheral portion. This asphericshape moderately weakens the positive refractive power in the peripheralportion of the fourth lens and makes it possible to control the angle ofoff-axial incident light rays properly. The aspheric shape is effectivenot only in correcting various aberrations but also in preventing a dropin the ratio of the brightness in the peripheral area of the image planeto that in its center area, namely relative illumination.

In the present invention, preferably the sixth lens has a meniscus shapewith a convex surface on the object side near the optical axis and itsaspheric object-side and image-side surfaces each have a pole-changepoint in a position off the optical axis. The existence of thepole-change point in a position off the optical axis, namely in the lensperipheral portion, means that both the surfaces in the peripheralportion of the lens are curved toward the object side. Due to theaspheric shapes, the refractive power continuously changes in the areafrom the center of the lens to its peripheral portion so that sphericalaberrations and field curvature are corrected, particularly in theperipheral portion.

In the present invention, preferably the aspheric image-side surface ofthe seventh lens has a pole-change point in a position off the opticalaxis. Due to the existence of the pole-change point, the image-sidesurface in the peripheral portion has a convex shape, so the negativerefractive power of the seventh lens weakens in the peripheral portionor changes to positive refractive power in the peripheral portion. Thisaspheric surface makes it easy to control the angle of a chief rayincident on the image sensor at each image height point. When theobject-side surface of the seventh lens is an aspheric surface withpositive refractive power in the peripheral portion, it brings about thesame effect.

In the present invention, a “pole-change point” here means a point on anaspheric surface at which a tangential plane intersects the optical axisperpendicularly.

Preferably the imaging lens according to the present invention satisfiesconditional expressions (6) and (7) below:

0.55<f12/f<0.88  (6)

−1.2<f3/f<−0.7  (7)

-   -   where    -   f: focal length of the overall optical system of the imaging        lens    -   f12: composite focal length of the first lens and the second        lens    -   f3: focal length of the third lens

The conditional expression (6) defines an adequate range for thecomposite focal length of the first lens and the second lens withrespect to the focal length of the overall optical system of the imaginglens. If the value is below the lower limit of the conditionalexpression (6), the composite positive refractive power of the firstlens and the second lens would be too strong, making it difficult tocorrect spherical aberrations, coma aberrations, and astigmatism, and ifit is above the upper limit, the composite positive refractive power ofthe first lens and the second lens would be too weak, making itdifficult to shorten the total track length.

The conditional expression (7) defines an adequate range for the focallength of the third lens with respect to the focal length of the overalloptical system of the imaging lens. If the value is below the lowerlimit of the conditional expression (7), the negative refractive powerof the third lens would be too weak, making it difficult to correctaxial chromatic aberrations, and if it is above the upper limit, thenegative refractive power of the third lens would be too strong, makingit difficult to shorten the total track length.

A more preferable range of the conditional expression (6) is aconditional expression (6a) below:

0.60<f12/f<0.80  (6a)

A more preferable range of the conditional expression (7) is aconditional expression (7a) below:

−1.05<f3/f<−0.70  (7a)

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the general configuration of animaging lens according to Example 1 of the invention;

FIG. 2 shows spherical aberration, astigmatism, and distortion of theimaging lens according to Example 1;

FIG. 3 is a schematic view showing the general configuration of animaging lens according to Example 2 of the invention;

FIG. 4 shows spherical aberration, astigmatism, and distortion of theimaging lens according to Example 2;

FIG. 5 is a schematic view showing the general configuration of animaging lens according to Example 3 of the invention;

FIG. 6 shows spherical aberration, astigmatism, and distortion of theimaging lens according to Example 3;

FIG. 7 is a schematic view showing the general configuration of animaging lens according to Example 4 of the invention;

FIG. 8 shows spherical aberration, astigmatism, and distortion of theimaging lens according to Example 4;

FIG. 9 is a schematic view showing the general configuration of animaging lens according to Example 5 of the invention; and

FIG. 10 shows spherical aberration, astigmatism, and distortion of theimaging lens according to Example 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, the preferred embodiments of the present invention will bedescribed in detail referring to the accompanying drawings. FIGS. 1, 3,5, 7, and 9 are schematic views showing the general configurations ofthe imaging lenses according to Examples 1 to 5 of an embodiment of thepresent invention respectively. Since all these examples have the samebasic configuration, a detailed explanation of an imaging lens accordingto the present embodiment is given below referring to the schematic viewof Example 1.

As shown in FIG. 1, in the imaging lens according to Example 1, lensesare arranged in the following order from an object side to an imageside: a first lens L1 with positive refractive power having a convexsurface on the object side near an optical axis X, a second lens L2 withpositive refractive power having convex surfaces on the object side andthe image side near the optical axis X, a third lens L3 with negativerefractive power having a concave surface on the image side near theoptical axis X, a fourth lens L4 having at least one aspheric surface, ameniscus fifth lens L5 having a concave surface on the object side nearthe optical axis X, a sixth lens L6 as a double-sided aspheric lens, anda seventh lens L7 as a double-sided aspheric lens with negativerefractive power having a concave surface on the image side near theoptical axis X. An aperture stop ST is located between the object-sidesurface apex of the second lens L2 and the peripheral edge of the samesurface. Also a filter IR such as an infrared cut filter is locatedbetween the seventh lens L7 and an image plane IM. In this embodiment,all lenses are made of plastic material and the first lens L1, thesecond lens L2, the fourth lens L4, the sixth lens L6, and the seventhlens L7 are made of a low-dispersion cycloolefin material and the thirdlens L3 and the fifth lens L5 are made of a high-dispersionpolycarbonate material.

In the above imaging lens, the positive refractive power of the secondlens L2 is stronger than that of the first lens L1 so that sphericalaberrations, astigmatism, and axial chromatic aberrations are corrected,and the positive refractive power of the second lens L2 is the strongestin the imaging lens so that the total track length is shortened. Boththe surfaces of each of the first lens L1 and the second lens L2 haveaspheric shapes to correct various aberrations properly. The first lensL1 is a meniscus lens which has a convex surface on the object side nearthe optical axis X and has peripheral portions curved toward the objectside on both the aspheric surfaces. The amount of spherical aberrationswhich occur on the peripheral portion of the biconvex second lens L2with strong refractive power is decreased by the aspheric shapes of thefirst lens L1. Also, field curvature is corrected in the area from anearly middle image height point to the maximum image height point.

The third lens L3 properly corrects residual axial chromatic aberrationswhich have not been corrected by the first lens L1 and the second lensL2. The third lens L3 is a meniscus lens having a concave surface on theimage side, in which both the surfaces are aspheric. The asphericobject-side surface of the lens changes to a concave shape in theperipheral portion, thereby preventing a drop in the quantity of lightarriving at the peripheral area of the image plane IM.

The fourth lens L4 corrects spherical aberrations, astigmatism, and comaaberrations through at least one aspheric surface formed thereon andalso plays an important role in reducing astigmatic difference. In thisembodiment, both the surfaces of the fourth lens L4 have aspheric shapesto correct various aberrations properly. The fourth lens L4 has abiconvex shape near the optical axis X and its image-side surface has anaspheric shape with a concave surface in the peripheral portion. Theaspheric shape of the image-side surface weakens the positive refractivepower in the peripheral portion in order to control the angle ofoff-axial incident light rays properly. This aspheric shape not onlycorrects various aberrations but also prevents a drop in the ratio ofthe brightness in the peripheral area of the image plane IM to that inits center area, namely relative illumination.

The fifth lens L5 is a meniscus lens which has the weakest positive ornegative refractive power in the imaging lens and it has a concavesurface on the object side. It is responsible for further correction ofaxial chromatic aberrations, proper correction of chromatic aberrationsof magnification and also correction of distortion on the image plane IMin the area from a low image height point to a nearly 80% image heightpoint.

The sixth lens L6 has aspheric shapes on both the surfaces and mainlycorrects spherical aberrations in the lens peripheral portion andastigmatism, particularly sagittal image surface curvature. It alsoadequately controls the angle of light rays emitted from the fifth lensL5 in the area from the low image height point to the maximum imageheight point. The sixth lens L6 has a meniscus shape with a convexsurface on the object side near the optical axis X, in which theaspheric surfaces on the object side and the image side each have apole-change point in a position off the optical axis X. In other words,the peripheral portion of the lens is curved toward the object side onboth the surfaces. Therefore, the refractive power continuously changesin the area from the center of the lens to its peripheral portion sothat spherical aberrations and field curvature are corrected,particularly in the lens peripheral portion.

The seventh lens L7 is a double-sided aspheric lens with negativerefractive power having a concave surface on the image side near theoptical axis X, making it easy to ensure an adequate back focus, correctastigmatism and control the chief ray angle (CRA) incident on the imagesensor. The seventh lens L7 has a biconcave shape near the optical axisX and its aspheric image-side surface has a pole-change point in aposition off the optical axis X. In other words, the image-side surfaceof the seventh lens L7 is an aspheric surface which is concave near theoptical axis X and gradually changes to a convex shape in the directiontoward the peripheral portion. Therefore, the negative refractive powerof the seventh lens L7 decreases in the direction toward the peripheralportion or changes to positive refractive power in the peripheralportion. This aspheric surface controls the angle of a chief rayincident on the image sensor at each image height point. In thisembodiment, the aspheric object-side surface of the seventh lens L7 isalso an aspheric surface in which the refractive power changes topositive refractive power in the peripheral portion. In other words, therequired positive refractive power in the peripheral portion of theseventh lens L7 is distributed to both the surfaces, so the asphericsurfaces do not need to have a sharp change in shape. If an asphericsurface has a sharp change in shape, it may be difficult to make anantireflection coating on it with uniform thickness. Especially, if theperipheral portion of the image-side surface of the seventh lens L7,located nearest to the image plane IM, has a shape sharply curved towardthe object side, the antireflection coating on the curved portion wouldbe thin and generation of unwanted light rays reflected by the innersurface of the curved portion would be likely to occur. If such unwantedlight rays are again reflected by the inner object-side surface of theseventh lens L7, they might enter the image plane IM, causing a ghostphenomenon.

The imaging lens according to the present invention satisfies thefollowing conditional expressions (1) to (7):

50<νd1<60  (1)

50<νd2<60  (2)

20<νd3<30  (3)

50<νd4<60  (4)

20<νd5<30  (5)

0.55<f12/f<0.88  (6)

−1.2<f3/f<−0.7  (7)

-   -   where    -   νd1: Abbe number of the first lens L1 at d-ray    -   νd2: Abbe number of the second lens L2 at d-ray    -   νd3: Abbe number of the third lens L3 at d-ray    -   νd4: Abbe number of the fourth lens L4 at d-ray    -   νd5: Abbe number of the fifth lens L5 at d-ray    -   f: focal length of the overall optical system of the imaging        lens    -   f12: composite focal length of the first lens L1 and the second        lens L2    -   f3: focal length of the third lens L3

The conditional expressions (1) to (5) define adequate ranges for theAbbe numbers of the first lens L1 to the fifth lens L5 respectively toensure that axial chromatic aberrations and chromatic aberrations ofmagnification are corrected properly. When these conditional expressionsare satisfied, readily available plastic materials can be used to reducecost.

In addition, when the composite focal length of the first lens L1 andthe second lens L2 and the focal length of the third lens L3 withrespect to the focal length of the overall optical system of the imaginglens fall within the adequate ranges defined by the conditionalexpressions (6) and (7) respectively, the total track length isshortened and various aberrations are corrected.

In this embodiment, all the lens surfaces are aspheric. The asphericshapes of these lens surfaces are expressed by the following equation,where Z represents an axis in the optical axis direction, H represents aheight perpendicular to the optical axis, k represents a conic constant,and A4, A6, A8, A10, A12, A14, and A16 represent aspheric surfacecoefficients.

$\begin{matrix}{Z = {\frac{\frac{H^{2}}{R}}{1 + \sqrt{1 - {\left( {k + 1} \right)\frac{H^{2}}{R^{2}}}}} + {A_{4}H^{4}} + {A_{6}H^{6}} + {A_{8}H^{8}} + {A_{10}H^{10}} + {A_{12}H^{12}} + {A_{14}H^{14}} + {A_{16}H^{16}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Next, the imaging lenses according to examples of the present embodimentwill be explained. In the description of each example, f represents thefocal length of the overall optical system of the imaging lens, Fnorepresents an F-number, ω represents a half field of view, ih representsa maximum image height, TTL represents a total track length without afilter IR, etc. i represents a surface number counted from the objectside, r represents a curvature radius, d represents the distance betweenlens surfaces on the optical axis X (surface distance), Nd represents arefractive index at d-ray (reference wavelength), and νd represents anAbbe number at d-ray. As for aspheric surfaces, an asterisk (*) aftersurface number i indicates that the surface concerned is an asphericsurface.

Example 1

The basic lens data of Example 1 is shown below in Table 1.

TABLE 1 Numerical Example 1 in mm f = 4.54 Fno = 1.64 ω(deg) = 32.3 ih =2.93 TTL = 5.39 Surface Data Curvature Surface Refractive Abbe SurfaceNo. i Radius r Distance d Index Nd Number νd (Object Surface) InfinityInfinity  1* 1.902 0.415 1.5346 56.160  2* 2.154 0.372  3 (Stop)Infinity −0.310  4* 2.804 0.835 1.5346 56.160  5* −4.629 0.025  6* 2.6350.281 1.6355 23.911  7* 1.229 0.215  8* 10.737 0.390 1.5346 56.160  9*−6.667 0.504 10* −2.053 0.475 1.6355 23.911 11* −2.334 0.033 12* 2.3350.392 1.5438 55.570 13* 5.444 0.504 14* −4.682 0.300 1.5438 55.570 15*4.277 0.060 16 Infinity 0.300 1.5168 64.198 17 Infinity 0.711 ImagePlane Infinity Lens Start Surface Focal Length Constituent Lens Data 1 119.339 2 4 3.399 3 6 −3.930 4 8 7.754 5 10 −78.686 6 12 7.201 7 14−4.062 Composite Focal Length f12 3.132 Aspheric Surface Data 1stSurface 2nd Surface 4th Surface 5th Surface 6th Surface k  0.000E+000.000E+00 0.000E+00 0.000E+00 −2.244E+01 A4 −2.585E−02 −3.053E−02 1.738E−02 8.350E−02 −7.495E−02 A6 −1.346E−02 −1.724E−02  −2.979E−03 −3.576E−02   4.811E−03 A8  3.021E−03 −1.056E−03  6.816E−03 3.944E−03 7.677E−03 A10 −7.914E−03 3.264E−04 −2.504E−04  5.485E−03 −4.413E−04 A12 3.743E−03 2.720E−04 −3.703E−04  −2.325E−03  −5.191E−04 A14 −5.404E−047.458E−05 4.421E−05 1.804E−04 −5.450E−09 A16 −8.605E−06 −5.306E−05 2.125E−05 7.832E−10 −2.786E−10 7th Surface 8th Surface 9th Surface 10thSurface 11th Surface k −5.106E+00 0.000E+00 0.000E+00 0.000E+00−1.360E+00 A4  2.786E−03 1.333E−01 1.166E−01 1.826E−01  2.895E−02 A6−2.679E−02 −2.718E−02  8.934E−03 −1.172E−01  −1.823E−02 A8  2.158E−02−2.275E−02  −2.356E−02  4.533E−02  1.721E−04 A10  2.014E−03 4.214E−036.432E−03 −5.340E−03   3.419E−03 A12 −8.549E−03 7.364E−03 8.451E−05−1.253E−03  −3.690E−04 A14  4.813E−03 −3.030E−03  −3.635E−04  2.332E−10 1.495E−05 A16 −3.777E−12 0.000E+00 0.000E+00 9.965E−12 −7.930E−05 12thSurface 13th Surface 14thSurface 15th Surface k −1.057E+01 0.000E+002.518E+00 −3.354E+01  A4 −6.430E−03 1.460E−02 −4.876E−02  −4.782E−02  A6−3.412E−02 −4.644E−02  1.146E−02 8.143E−03 A8  6.072E−03 1.435E−027.163E−04 −6.599E−04  A10  2.003E−04 −2.257E−03  −7.095E−05  2.774E−05A12 −3.274E−05 1.691E−04 −2.653E−05  −1.581E−06  A14 −5.291E−061.634E−06 2.233E−07 −9.307E−07  A16  1.691E−06 5.860E−07 4.051E−071.710E−07

As shown in Table 6, the imaging lens according to Example 1 satisfiesall the conditional expressions (1) to (7).

FIG. 2 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens according to Example 1. The spherical aberrationgraph shows the amount of aberration at wavelengths of g-ray (436 nm),F-ray (486 nm), e-ray (546 nm), d-ray (588 nm), and C-ray (656 nm). Theastigmatism graph shows the amount of aberration on sagittal imagesurface S and the amount of aberration on tangential image surface T(the same is true for FIGS. 4, 6, 8, and 10 which correspond to Examples2 to 5 respectively). As FIG. 2 suggests, various aberrations areproperly corrected.

Example 2

The basic lens data of Example 2 is shown below in Table 2.

TABLE 2 Numerical Example 2 in mm f = 4.57 Fno = 1.61 ω(deg) = 32.3 ih =2.93 TTL = 5.38 Surface Data Curvature Surface Refractive Abbe SurfaceNo. i Radius r Distance d Index Nd Number νd (Object Surface) InfinityInfinity  1* 1.953 0.411 1.5346 56.160  2* 2.225 0.346  3 (Stop)Infinity −0.310  4* 2.745 0.864 1.5346 56.160  5* −4.089 0.025  6* 2.6620.290 1.6355 23.911  7* 1.191 0.257  8* 10.737 0.404 1.5346 56.160  9*−6.667 0.541 10* −2.006 0.472 1.6355 23.911 11* −2.227 0.025 12* 2.5620.393 1.5438 55.570 13* 5.661 0.500 14* −4.423 0.301 1.5438 55.570 15*4.284 0.060 16 Infinity 0.300 1.5168 64.198 17 Infinity 0.610 ImagePlane Infinity Lens Start Surface Focal Length Constituent Lens Data 1 119.597 2 4 3.214 3 6 −3.676 4 8 7.756 5 10 −184.069 6 12 8.241 7 14−3.953 Composite Focal Length f12 2.984 Aspheric Surface Data 1stSurface 2nd Surface 4th Surface 5th Surface 6th Surface k  0.000E+000.000E+00 0.000E+00 0.000E+00 −2.399E+01 A4 −2.588E−02 −3.045E−02 1.627E−02 8.497E−02 −7.432E−02 A6 −1.344E−02 −1.724E−02  −3.376E−03 −3.529E−02   5.948E−03 A8  3.083E−03 −1.075E−03  6.697E−03 4.166E−03 8.369E−03 A10 −7.891E−03 3.276E−04 −3.162E−04  5.606E−03 −2.317E−04 A12 3.747E−03 2.744E−04 −3.939E−04  −2.260E−03  −5.540E−04 A14 −5.404E−047.486E−05 4.678E−05 2.208E−04 −7.923E−06 A16 −7.675E−06 −5.309E−05 3.204E−05 −5.373E−06  −9.315E−09 7th Surface 8th Surface 9th Surface10th Surface 11th Surface k −4.941E+00 0.000E+00 0.000E+00 0.000E+00−1.532E+00 A4  4.462E−03 1.333E−01 1.166E−01 1.762E−01  2.971E−02 A6−2.683E−02 −2.718E−02  8.934E−03 −1.184E−01  −2.115E−02 A8  2.167E−02−2.275E−02  −2.356E−02  4.596E−02 −2.925E−04 A10  3.019E−03 4.214E−036.432E−03 −5.690E−03   3.660E−03 A12 −8.594E−03 7.364E−03 8.451E−05−1.236E−03  −2.149E−04 A14  4.813E−03 −3.030E−03  −3.635E−04  1.522E−04 2.478E−05 A16 −7.587E−09 0.000E+00 0.000E+00 5.674E−09 −1.107E−04 12thSurface 13th Surface 14th Surface 15th Surface k −1.419E+01 0.000E+002.050E+00 −2.517E+01  A4 −1.160E−02 6.647E−03 −4.529E−02  −5.781E−02  A6−3.634E−02 −4.470E−02  1.102E−02 1.019E−02 A8  7.211E−03 1.442E−027.039E−04 −6.975E−04  A10  3.787E−04 −2.277E−03  −8.623E−05  1.016E−05A12 −5.306E−05 1.607E−04 −2.641E−05  −3.909E−06  A14 −2.594E−051.246E−06 2.578E−07 −1.033E−06  A16 −5.533E−06 6.751E−07 4.090E−071.969E−07

As shown in Table 6, the imaging lens according to Example 2 satisfiesall the conditional expressions (1) to (7).

FIG. 4 shows spherical aberration, astigmatism, and distortion of theimaging lens according to Example 2. As FIG. 4 suggests, variousaberrations are properly corrected.

Example 3

The basic lens data of Example 3 is shown below in Table 3.

TABLE 3 Numerical Example 3 in mm f = 4.35 Fno = 1.61 ω(deg) = 33.5 ih =2.93 TTL = 5.29 Surface Data Curvature Surface Refractive Abbe SurfaceNo. i Radius r Distance d Index Nd Number νd (Object Surface) InfinityInfinity  1* 1.811 0.435 1.5346 56.160  2* 2.061 0.379  3 (Stop)Infinity −0.310  4* 2.972 0.757 1.5346 56.160  5* −4.842 0.026  6* 2.7390.280 1.6355 23.911  7* 1.327 0.210  8* 10.737 0.392 1.5346 56.160  9*−6.667 0.443 10* −2.288 0.483 1.6355 23.911 11* −2.741 0.025 12* 2.5220.509 1.5438 55.570 13* 6.671 0.495 14* −4.708 0.300 1.5438 55.570 15*4.458 0.060 16 Infinity 0.300 1.5168 64.198 17 Infinity 0.611 ImagePlane Infinity Lens Start Surface Focal Length Constituent Lens Data 1 117.392 2 4 3.565 3 6 −4.391 4 8 7.755 5 10 −37.202 6 12 7.147 7 14−4.163 Composite Focal Length f12 3.223 Aspheric Surface Data 1stSurface 2nd Surface 4th Surface 5th Surface 6th Surface k  0.000E+000.000E+00 0.000E+00 0.000E+00 −2.079E+01 A4 −2.541E−02 −3.036E−02 1.723E−02 8.057E−02 −7.974E−02 A6 −1.294E−02 −1.835E−02  −7.877E−04 −3.527E−02   8.318E−04 A8  2.519E−03 −1.075E−03  6.396E−03 4.455E−03 6.390E−03 A10 −8.191E−03 1.662E−04 −1.598E−04  5.365E−03  3.628E−04 A12 3.676E−03 1.087E−04 −1.465E−04  −2.077E−03   2.432E−04 A14 −5.541E−041.381E−05 5.068E−05 3.349E−04 −1.814E−10 A16 −1.560E−05 −4.163E−05 1.269E−06 9.495E−11 −8.206E−11 7th Surface 8th Surface 9th Surface 10thSurface 11th Surface k −5.518E+00 0.000E+00 0.000E+00 0.000E+00−2.430E+00 A4 −3.273E−03 1.333E−01 1.166E−01 1.782E−01  2.990E−02 A6−3.079E−02 −2.718E−02  8.934E−03 −1.101E−01  −2.219E−02 A8  1.859E−02−2.275E−02  −2.356E−02  3.986E−02  1.953E−03 A10  3.980E−03 4.214E−036.432E−03 −4.996E−03   3.378E−03 A12 −8.549E−03 7.364E−03 8.451E−05−1.086E−03  −6.961E−04 A14  4.813E−03 −3.030E−03  −3.635E−04 −7.581E−11  −2.481E−05 A16  5.236E−12 0.000E+00 0.000E+00 6.501E−12−4.169E−05 12th Surface 13th Surface 14th Surface 15th Surface k−1.042E+01 0.000E+00 2.886E+00 −2.941E+01  A4 −1.359E−02 2.248E−02−4.729E−02  −4.789E−02  A6 −3.048E−02 −4.633E−02  1.124E−02 7.971E−03 A8 4.457E−03 1.394E−02 6.397E−04 −6.186E−04  A10 −2.316E−05 −2.365E−03 −8.194E−05  4.033E−05 A12 −8.171E−05 1.547E−04 −2.782E−05  −3.314E−07 A14 −2.648E−05 −6.468E−07  −4.383E−08  −1.067E−06  A16 −1.689E−061.539E−07 3.462E−07 6.428E−08

As shown in Table 6, the imaging lens according to Example 3 satisfiesall the conditional expressions (1) to (7).

FIG. 6 shows spherical aberration, astigmatism, and distortion of theimaging lens according to Example 3. As FIG. 6 suggests, variousaberrations are properly corrected.

Example 4

The basic lens data of Example 4 is shown below in Table 4.

TABLE 4 Numerical Example 4 in mm f = 4.67 Fno = 1.61 ω(deg) = 31.7 ih =2.93 TTL = 5.53 Surface Data Curvature Surface Refractive Abbe SurfaceNo. i Radius r Distance d Index Nd Number νd (Object Surface) InfinityInfinity  1* 1.947 0.423 1.5346 56.160  2* 2.195 0.342  3 (Stop)Infinity −0.310  4* 2.907 0.852 1.5346 56.160  5* −4.062 0.056  6* 2.9860.305 1.6355 23.911  7* 1.210 0.220  8* 10.737 0.389 1.5346 56.160  9*−6.667 0.535 10* −2.463 0.478 1.6355 23.911 11* −2.600 0.025 12* 2.2360.382 1.5438 55.570 13* 4.264 0.580 14* −4.975 0.300 1.5438 55.570 15*4.893 0.060 16 Infinity 0.300 1.5168 64.198 17 Infinity 0.703 ImagePlane Infinity Lens Start Surface Focal Length Constituent Lens Data 1 120.244 2 4 3.311 3 6 −3.432 4 8 7.754 5 10 210.517 6 12 8.111 7 14−4.488 Composite Focal Length f12 3.081 Aspheric Surface Data 1stSurface 2nd Surface 4th Surface 5th Surface 6th Surface k  0.000E+000.000E+00 0.000E+00 0.000E+00 −3.171E+01  A4 −2.514E−02 −2.981E−02 1.517E−02 8.718E−02 −7.635E−02  A6 −1.267E−02 −1.795E−02  −1.896E−03 −3.512E−02  5.147E−03 A8  2.965E−03 −1.062E−03  6.378E−03 4.702E−038.248E−03 A10 −7.975E−03 2.531E−04 −3.606E−04  5.885E−03 1.080E−04 A12 3.739E−03 1.878E−04 −3.374E−04  −1.900E−03  −6.483E−04  A14 −5.366E−044.815E−05 1.398E−05 6.850E−05 7.455E−09 A16 −1.151E−05 −3.502E−05 5.232E−05 −1.702E−10  3.540E−09 7th Surface 8th Surface 9th Surface 10thSurface 11th Surface k −5.117E+00 0.000E+00 0.000E+00 0.000E+00−1.779E+00  A4  5.084E−03 1.333E−01 1.166E−01 1.648E−01 3.002E−02 A6−2.680E−02 −2.718E−02  8.934E−03 −1.034E−01  −1.928E−02  A8  1.936E−02−2.275E−02  −2.356E−02  4.037E−02 1.610E−03 A10  2.465E−03 4.214E−036.432E−03 −6.220E−03  3.245E−03 A12 −8.552E−03 7.364E−03 8.451E−05−6.714E−04  −6.733E−04  A14  4.810E−03 −3.030E−03  −3.635E−04  2.031E−047.039E−06 A16 −7.751E−15 0.000E+00 0.000E+00 −2.461E−08  −2.005E−05 12th Surface 13th Surface 14th Surface 15th Surface k −7.605E+000.000E+00 2.911E+00 −4.208E+01  A4 −3.902E−03 1.529E−02 −5.099E−02 −4.642E−02  A6 −2.818E−02 −4.334E−02  1.168E−02 6.574E−03 A8  5.029E−031.402E−02 7.135E−04 −5.918E−04  A10  4.479E−05 −2.336E−03  −6.781E−05 5.885E−05 A12 −1.233E−05 1.720E−04 −2.534E−05  3.887E−07 A14 −2.613E−061.772E−06 2.218E−07 −8.690E−07  A16  4.552E−07 −1.893E−08  3.522E−071.116E−07

As shown in Table 6, the imaging lens according to Example 4 satisfiesall the conditional expressions (1) to (7).

FIG. 8 shows spherical aberration, astigmatism, and distortion of theimaging lens according to Example 4. As FIG. 8 suggests, variousaberrations are properly corrected.

Example 5

The basic lens data of Example 5 is shown below in Table 5.

TABLE 5 Numerical Example 5 in mm f = 4.52 Fno = 1.61 ω(deg) = 32.5 ih =2.93 TTL = 5.39 Surface Data Curvature Surface Refractive Abbe SurfaceNo. i Radius r Distance d Index Nd Number νd (Object Surface) InfinityInfinity  1* 1.932 0.416 1.5346 56.160  2* 2.205 0.356  3 (Stop)Infinity −0.310  4* 2.830 0.825 1.5438 55.570  5* −4.537 0.025  6* 2.6740.281 1.6355 23.911  7* 1.225 0.227  8* 10.737 0.391 1.5438 55.570  9*−6.667 0.516 10* −2.020 0.502 1.6142 25.577 11* −2.331 0.027 12* 2.4110.431 1.5438 55.570 13* 5.386 0.492 14* −5.074 0.300 1.5438 55.570 15*4.201 0.060 16 Infinity 0.300 1.5168 64.198 17 Infinity 0.661 ImagePlane Infinity Lens Start Surface Focal Length Constituent Lens Data 1 119.037 2 4 3.337 3 6 −3.848 4 8 7.624 5 10 −63.587 6 12 7.636 7 14−4.178 Composite Focal Length f12 3.071 Aspheric Surface Data 1stSurface 2nd Surface 4th Surface 5th Surface 6th Surface k  0.000E+000.000E+00 0.000E+00  0.000E+00 −2.363E+01 A4 −2.581E−02 −3.076E−02 1.753E−02  8.382E−02 −7.444E−02 A6 −1.347E−02 −1.720E−02  −3.147E−03 −3.551E−02  5.772E−03 A8  3.083E−03 −1.057E−03  6.771E−03  3.978E−03 7.923E−03 A10 −7.892E−03 3.389E−04 −3.134E−04   5.493E−03  2.625E−04A12  3.742E−03 2.804E−04 −4.051E−04  −2.306E−03 −8.276E−04 A14−5.421E−04 7.598E−05 4.239E−05  2.229E−04  2.057E−07 A16 −7.174E−06−5.350E−05  3.405E−05 −1.593E−08 −1.165E−10 7th Surface 8th Surface 9thSurface 10th Surface 11th Surface k −5.113E+00 0.000E+00 0.000E+00 0.000E+00 −1.241E+00 A4  3.365E−03 1.333E−01 1.166E−01  1.803E−01 2.747E−02 A6 −2.559E−02 −2.718E−02  8.934E−03 −1.183E−01 −2.152E−02 A8 2.200E−02 −2.275E−02  −2.356E−02   4.581E−02  4.305E−04 A10  2.594E−034.214E−03 6.432E−03 −3.826E−03  3.976E−03 A12 −8.566E−03 7.364E−038.451E−05 −1.811E−03 −3.477E−04 A14  4.791E−03 −3.030E−03  −3.635E−04 −3.018E−05  1.946E−05 A16  1.044E−10 0.000E+00 0.000E+00  1.393E−04−8.192E−05 12th Surface 13th Surface 14th Surface 15th Surface k−1.134E+01 0.000E+00 1.286E+00 −2.974E+01 A4 −1.147E−02 5.069E−03−6.218E−02  −5.562E−02 A6 −3.964E−02 −4.732E−02  1.439E−02  1.107E−02 A8 7.440E−03 1.442E−02 −1.796E−04  −1.025E−03 A10  3.038E−04 −2.197E−03 5.922E−07  4.355E−05 A12 −1.288E−04 1.423E−04 −2.141E−05  −6.258E−06 A14−3.962E−07 −5.039E−07  1.447E−06 −8.289E−07 A16  2.395E−06 2.550E−064.262E−08  2.121E−07

As shown in Table 6, the imaging lens according to Example 5 satisfiesall the conditional expressions (1) to (7).

FIG. 10 shows spherical aberration, astigmatism, and distortion of theimaging lens according to Example 5. As FIG. 10 suggests, variousaberrations are properly corrected.

As mentioned above, the imaging lenses according to Examples 1 to 5provide brightness with an F-value of about 1.6 and improvedperformance. Although the seven constituent lenses are not joined toeach other, the total track length is as short as about 5.5 mm, which isshorter than the diagonal length of the effective image plane of theimage sensor.

Table 6 shows data on Examples 1 to 5 of the embodiment relating to theconditional expressions (1) to (7).

TABLE 6 Values of Exam- Exam- Exam- Exam- Exam- Conditional Expressionsple 1 ple 2 ple 3 ple 4 ple 5 (1) 50 < vd1 < 60 56.160 56.1603 56.160356.1603 56.1603 (2) 50 < vd2 < 60 56.160 56.1603 56.1603 56.1603 55.5699(3) 20 < vd3 < 30 23.911 23.9114 23.9114 23.9114 23.9114 (4) 50 < vd4 <60 56.160 56.160 56.160 56.160 55.570 (5) 20 < vd5 < 30 23.911 23.91123.911 23.911 25.577 (6) 0.55 < f12/f < 0.88 0.690 0.654 0.741 0.6600.680 (7) −1.2 < f3/f < −0.7 −0.866 −0.805 −1.010 −0.735 −0.852

As explained above, when the imaging lens according to any of theaforementioned examples is used for an optical system built in an imagepickup device mounted in an increasingly compact and low-profile mobileterminal such as a smart phone, mobile phone or PDA (Personal DigitalAssistant), or a game console or information terminal such as a PC, itprovides a compact high-performance camera function.

The effects of the present invention are as follows. According to thepresent invention, it is possible to provide a compact imaging lenswhich corrects various aberrations properly with a small F-value. Also,when plastic material is used for the constituent lenses as much aspossible, the imaging lens can be mass-produced at low cost.

What is claimed is:
 1. A fixed-focus imaging lens composed of sevenlenses to form an image of an object on a solid-state image sensor, inwhich the lenses are arranged in order from an object side to an imageside, comprising: a first lens with positive refractive power having aconvex surface on the object side near an optical axis; a second lenswith positive refractive power having convex surfaces on the object sideand the image side near the optical axis; a third lens with negativerefractive power having a concave surface on the image side near theoptical axis; a fourth lens having at least one aspheric surface; ameniscus fifth lens having a concave surface on the object side near theoptical axis; a sixth lens as a double-sided aspheric lens; and aseventh lens as a double-sided aspheric lens with negative refractivepower having a concave surface on the image side near the optical axis,wherein the lenses are not joined to each other.
 2. The imaging lensaccording to claim 1, wherein the first lens has a meniscus shape nearthe optical axis and both surfaces thereof have aspheric shapes withperipheral portions thereof curved toward the object side.
 3. Theimaging lens according to claim 1, wherein conditional expressions (1),(2), and (3) below are satisfied:50<νd1<60  (1)50<νd2<60  (2)20<νd3<30  (3) where νd1: Abbe number of the first lens at d-ray νd2:Abbe number of the second lens at d-ray νd3: Abbe number of the thirdlens at d-ray
 4. The imaging lens according to claim 3, whereinconditional expressions (4) and (5) below are satisfied:50<νd4<60  (4)20<νd5<30  (5) where νd4: Abbe number of the fourth lens at d-ray νd5:Abbe number of the fifth lens at d-ray
 5. The imaging lens according toclaim 1, wherein the fourth lens has a biconvex shape near the opticalaxis and the image-side surface thereof has an aspheric shape with aconcave surface in a peripheral portion thereof.
 6. The imaging lensaccording to claim 1, wherein the sixth lens has a meniscus shape with aconvex surface on the object side near the optical axis and the asphericobject-side and image-side surfaces thereof each have a pole-changepoint.
 7. The imaging lens according to claim 1, wherein the image-sidesurface of the seventh lens is an aspheric surface with a pole-changepoint.
 8. The imaging lens according to claim 1, wherein conditionalexpressions (6) and (7) below are satisfied:0.55<f12/f<0.88  (6)−1.2<f3/f<−0.7  (7) where f: focal length of the overall optical systemof the imaging lens f12: composite focal length of the first lens andthe second lens f3: focal length of the third lens
 9. The imaging lensaccording to claim 2, wherein conditional expressions (1), (2), and (3)below are satisfied:50<νd1<60  (1)50<νd2<60  (2)20<νd3<30  (3) where νd1: Abbe number of the first lens at d-ray νd2:Abbe number of the second lens at d-ray νd3: Abbe number of the thirdlens at d-ray
 10. The imaging lens according to claim 9, whereinconditional expressions (4) and (5) below are satisfied:50<νd4<60  (4)20<νd5<30  (5) where νd4: Abbe number of the fourth lens at d-ray νd5:Abbe number of the fifth lens at d-ray
 11. The imaging lens according toclaim 2, wherein the fourth lens has a biconvex shape near the opticalaxis and the image-side surface thereof has an aspheric shape with aconcave surface in a peripheral portion thereof.
 12. The imaging lensaccording to claim 2, wherein the sixth lens has a meniscus shape with aconvex surface on the object side near the optical axis and the asphericobject-side and image-side surfaces thereof each have a pole-changepoint.
 13. The imaging lens according to claim 2, wherein the image-sidesurface of the seventh lens is an aspheric surface with a pole-changepoint.
 14. The imaging lens according to claim 2, wherein conditionalexpressions (6) and (7) below are satisfied:0.55<f12/f<0.88  (6)−1.2<f3/f<−0.7  (7) where f: focal length of the overall optical systemof the imaging lens f12: composite focal length of the first lens andthe second lens f3: focal length of the third lens